The answer, it seems, is only from Windows Unified Data Storage Server 2003, which goes by so many other names, it can be challenging to understand sometimes. However, the Single Instance Store, which is based on the Exchange and WDS technologies, detects multiple copies of the same document and consolidates them to a single document with mulitple pointers. However, this feature is NOT available on any other edition of Windows Server. Of course, this isn't well documented, as I tried to find out yesterday when doing a feature comparison.
SIS is not part of Windows Server 2003 Standard, Enterprise or Datacenter (or Web), 32 or 64 bit. SIS is not part of Windows Server 2008; ditto on the variations. SIS is only available on WUDSS, which is, as of this writing, only available on the 2003 R2 platform.
A version of Unified Data Storage Server (WUDSS) will be released in 2009 on the Windows Server 2008 platform and that specific SKU will have SIS incorporated into it.